Toxicity of Local Anaesthesia

Toxicity can be categorised as either local or systemic:

Local toxicity includes:

• Infection


• Haematoma


• Local tissue damage e.g. intraneural injection


• Unwanted nerve block


• Necrosis through ischaemia from vasoconstrictor


• Pneumothorax (in blocks around the neck or axilla)

Systemic toxicity:

Cardiovascular toxicity includes:

• Cardiac depression – reduced BP, tachycardia, reduced cardiac output and acute cardiac dilatation


• Peripheral vasodilatation, except cocaine–vasoconstriction

Respiratory toxicity includes:

• Medullary depression


• Bronchospasm from hypersensitivity – although extremely rare. Bronchospasm may also be induced in those with a psychogenic element to their illness such as in some asthma sufferers


• Relaxation of bronchial musculature

With CNS toxicity:

• The higher cortex tends to be excited whereas the mid-brain is depressed


• Loss of inhibitory neurones leads to cortical excitability, e.g. fits or tremor


• Depression of the mid-brain leads to respiratory collapse.

Non-specific toxicity includes

• Methaemoglobinaemia (with prilocaine)


• Hypersensitivity reactions:
  
  
  
  • The preservative methylparaben, used in multidose vials may cause such reactions
  
  
  • Reactions may be local (rash/dermatitis) or generalised
  
  
  • All reactions are unusual; true anaphylaxis is extremely rare and has only been reported in individual case reports. It has been suggested that patients who declare that they are ‘allergic’ should be skin tested, but this should only be considered in those who can describe a clear history of severe reaction. Many cases of ‘allergy’ involving collapse can be attributed to vasovagal faints, and mechanisms not related to hypersensitivity
  
  
  
  


• Intravenous injections


• Psychological reactions e.g. anxiety leading to vasovagal collapse

Toxicity of Local Anaesthesia